Attached backtrace from ubuntu 16.04 (firefox 53.0+build6-0ubuntu0.16.04.1, conkeror
1.0.3+git170412+2207-~nightly1) triggered by "click on any link in a mail message in Gmail", for another
example. (Rolling back to firefox-esr worked, confirming at least that the problem is along that upgrade
boundary.)

From what I can understand in the referenced bug, somewhere we need to call
browser.presetOpenerWindow(aOpener); in the openuri function.
I tried to put the following patch:
modified modules/content-buffer.js
@@ -615,6 +615,9 @@ browser_dom_window.prototype = {
/* Determine the opener buffer */
var opener = get_buffer_from_frame(this.window, aOpener);
+ if (aOpener) {
+ this.browser.presetOpenerWindow(aOpener);
+ }
switch (browser_default_open_target) {
case OPEN_CURRENT_BUFFER:
And that fixes the crash - though I have issues to open links from gmail for
example, a dialog box is shown telling that there is probably a popup blocker
preventing to open the page and the page is not displayed;
I am not sure if I can help more with my current knowledge, as I don't really
understand what I am doing here. :) Scott, maybe you understand better than me
and you have some time to look into it ? Else I might ask some help on the
mozilla irc.

Julien,
Well if that prevents conkeror from crashing that's pretty nice even if it doesn't work in the situations
where it would have crashed.
Unfortunately I don't understand the issue any better than you. I did try a few minor changes but wasn't
able to get a fix.
I'haven't had any luck with the mozilla IRC in the past, and I don't think there are going to be many
people willing to take a close enough look at a project they don't use.
Our best hope is that a conkeror user or past contributor out there decides to do a deep dive into this.
As more and more people upgrade to ff53, or when ff59 comes out and ESR users upgrade, there may be
someone who figures out a fix and submits it.
You could send an email to the conkeror mailing list letting some of these people know about the issue.
If no fix is forthcoming, you may consider running firefox 52 which luckily is an ESR so should be
supported until ff59.
Cheers

Julien, your patch above is just inserting an error into browser_dom_window.openURI - there is no
property 'this.browser'. So any error, or perhaps a simple 'return null;' at that point may reproduce
the 'fix' you see. I would be curious to know what behavior results from 'return null;' at that point.
From my reading though, what Michael Layzell indicated is that opener needs to be set on the new window,
not the old one. Scott and I tried a couple of ways of doing exactly that, and the crash remained, so in
my view, this crash that we're seeing is the one from
https://bugzilla.mozilla.org/show_bug.cgi?id=1334086 not the one from
https://bugzilla.mozilla.org/show_bug.cgi?id=1316104